Multicarrier modulation techniques, such as frequency division multiplexing (FDM), have become widely used in many high-speed communication applications. In multicarrier modulation, a multichannel digital transmitter simultaneously frequency translates a number of baseband signals into a set of carrier-band channels in a single wideband composite signal. A receiver may demodulate one or more of the channels of the wideband composite signal to the baseband.
One notable application of multicarrier modulation is cable television transmission. A cable television waveform is formed by frequency translating multiple baseband signals to a set of carrier channels, each baseband signal representing one television signal. Each baseband signal is placed at a unique center frequency of a respective channel according to an FDM mapping scheme.
Multichannel modulation devices may employ various topologies and architectures. In one approach, modulation circuitry is duplicated for each channel. A composite wideband signal is generated from several carrier band signals using multiple up-converter circuits, one for each baseband channel. This approach offers a large degree of freedom on how pulse shaping and up-conversion are managed for each channel. As a result, the modulation of each channel may be set to adjust the center frequency, bandwidth, and channel spacing independent of the other channels. However, this approach is computationally expensive and may be prohibitive as the number of channels increases.
Another modulation technique utilizes polyphase filter banks to simultaneously place the baseband signals on a set of equally spaced channels. In this approach, a Fourier transform is performed in combination with polyphase filtering. The Fourier transform synthesizes a series of narrow bandwidth channels. A polyphase filter rejects extraneous spectral images of the baseband signals and shapes the bandwidth of the baseband signals in the channels. A combiner assembles a single wideband composite signal. Existing polyphase filter banks require a strict coupling between the sample rate of each baseband channel, the Fourier transform length (typically equaling the number of baseband signals), the frequency spacing of the channels in the composite wideband signal, and the sample rate of the composite wideband signal.
One or more embodiments may address one or more of the above issues.